Optical disc device, circuit for optical disc device, wobble signal reproduction method, and land pre-pit signal reproduction method

ABSTRACT

A mark S/H circuit ( 66 ) samples, for example, a signal A generated as a photodetector ( 20 ) detects a return beam from marks of an optical disk ( 10 ), a space S/H circuit ( 68 ) samples a signal A generated through detection of a return beam from spaces, and amplifiers ( 70  and  72 ) justify amplitudes of the sampled A signals from the marks and spaces. A mark/space selector switch ( 74 ) selects alternately and combines the mark and space signals whose amplitudes have been justified. After A, B, C, and D signals A 1  to D 1  are subjected individually to a series of processes up to the combination process, a wobble processing circuit ( 80 ) adds them in predetermined combinations, finds differences among the added signals after justifying the amplitudes of the added signals, and thereby reproduces a wobble signal ( 107 ).

TECHNICAL FIELD

The present invention relates to an optical disk device which recordsand plays back documents, images, music, or other data on/from anoptical disk. More particularly, it relates to an optical disk device,circuit for an optical disk device, wobble signal reproduction method,and land pre-pit signal reproduction method suitable for detecting andreproducing a wobble signal and LPP (land pre-pit) signal recorded on arecordable/reproducible optical disk.

BACKGROUND ART

Currently, CD-R/RW, DVD-R/RW, DVD+R/RW, and the like are available asoptical disks capable of high-density recording. When recordinginformation on these recordable optical disks, a reference clock signalfor writes cannot be generated from a reproduction signal used onconventional read-only disks.

Thus, a recordable optical disk is configured as shown in FIG. 8. FIG. 8shows part of a DVD-R/RW disk surface. Grooves 12 for use to recordinformation are formed spirally on the optical disk (hereinafterinterchangeably referred to as a DVD-R/RW) 10, wobbling periodicallywith a fixed amplitude. They are called wobbles.

The grooves 12 are designed such that large volumes of pit data 14 whichrepresent various information are written into it. Also, notches calledland pre-pits (hereinafter referred to as LPP) 18 are provided in eachland 16 between a groove 12 and groove 12 as also shown in FIG. 9.

Light reflected by the wobbling grooves 12 irradiated with a laser spotis detected by a four-part photodetector (split-type optical sensor) 20in a push-pull fashion. Consequently, difference in light quantities isdetected. The detected signal is called a wobble signal. A referenceclock signal for writes can be generated from the wobble signal.

No address information is superimposed on the wobble signal of theoptical disk 10 and an LPP signal obtained from the LPP 18 is used asaddress information. Where the LPP 18 is formed, the land isdiscontinuous. Consequently, the quantity of light entering thephotodetector 20 increases sharply when the laser spot passes throughthe discontinuous part and as a result of push-pull operation, a pulsedsignal is superimposed as the LPP signal on the wobble signal.

The wobble signal and LPP signal are used to control the rotationalspeed of the optical disk 10 and provide positional information.Recording/playback apparatus for optical disks 10 must detect thesignals with high accuracy.

Generally, signals A, B, C, and D read from the optical disk 10 by thephotodetector 20 have the following relationships. The wobble signal andLPP signal are extracted using arithmetic operations based on theserelationships. On the optical disk 10 after recording, the A, B, C, andD signals contain an RF signal (waveform signal) component whichrepresents difference in reflectance between marks 12 a (i.e., pit data14 in FIG. 8) and spaces 12 b.

A=RF signal+first wobble signal+LPP signal

B=RF signal+second wobble signal (opposite in phase to the first wobblesignal)

C=RF signal+second wobble signal (opposite in phase to the first wobblesignal)

D=RF signal+first wobble signal+LPP signal

The RF signals in all the A, B, C, and D signals have the same phase andbasically the same amplitude. The wobble signals in the A and D signalsare opposite in phase to the wobble signals in the B and C signals. TheLPP signal occurs only in the A and D signals (or B and C signals).

Due to these relationships, the arithmetic operation of (A+D)−(B+C) inprinciple cancels out the equiphase components, i.e., RF signals,leaving only the wobble signals and LPP signals. This is expressed asfollows.(A+D)−(B+C)

=(RF signal+first wobble signal+LPP signal+RF signal+first wobblesignal+LPP signal)−(RF signal+second wobble signal+RF signal+secondwobble signal)

=2×(RF signal+LPP signal+first wobble signal)−2×(RF signal+second wobblesignal)

=2×LPP signal+4×first wobble signal (this is because the first wobblesignal and second wobble signal are opposite in phase, and thus “firstwobble signal=−second wobble signal”)

Actually, however, due to variations in the sensitivity of thephotodetector 20 as well as variations in amplifier gain, the A+D signaland B+C signal are not exactly equal in amplitude components of the RFsignals. Therefore, the arithmetic operation is performed afterequalizing the amplitude components of the RF signals by adjusting thegains of A+D signal and B+C signal. AGC (Automatic Gain Control)amplifiers are often used for the gain adjustment and are configured asin the case of a wobble processing circuit 30 shown in FIG. 11.

In the wobble processing circuit 30, an adder 31 adds the A signal and Dsignal while an adder 32 adds the B signal and C signal. An AGCamplifier 34 adjusts the gain of the A+D signal outputted from the adder31 while an AGC amplifier 35 adjusts the gain of the B+C signaloutputted from the adder 32. That is, the gains are adjusted in such away as to equalize the amplitude components of the RF signals betweenthe A+D signal and B+C signal. Then, a subtractor 37 subtracts the B+Csignal from the A+D signal to output the (A+D)−(B+C), i.e., the wobblesignal and LPP signal.

However, the optical disk 10 is recorded by changing light quantitybetween the marks 12 a and spaces 12 b according to recording data.Consequently, the wobble signal and LPP signal cannot be reproduced bysimply detecting beams returning from the optical disk 10.

To deal with this situation, an S/H wobble processing circuit 40 isconfigured by connecting S/H (sample/hold) circuits 41 to 44 to theinput side of the wobble processing circuit 30 as shown in FIG. 12.

Operation of the S/H wobble processing circuit 40 will be described withreference to a timing chart shown in FIG. 13. It is assumed here thatthe optical disk 10 is a compact disk.

First, during recording, in a segment in which recording data shown in(1) is High, i.e., in a segment of High state which specifies a mark 12a to be formed (in a mark segment), a laser beam directed at the opticaldisk 10 becomes strong corresponding to the High state to provide writepower. That is, a waveform of a writing beam shown in (2) goes High,forming a mark 12 a on the optical disk 10. In so doing, a waveform of areturn beam used to read the A, B, C, and D signals goes High by risingsharply as shown in (3).

On the other hand, in a segment in which the recording data (1) is Low,i.e., in a segment of Low state which specifies a space 12 b to beformed (in a space segment), a laser beam directed at the optical disk10 becomes weak corresponding to the Low state to provide read power.That is, the waveform of the writing beam (2) goes Low. In this case,the waveform of the return beam is Low as shown in (3).

As the photodetector 20 detects the return beam with such a waveform asthe one shown in (3), the S/H wobble processing circuit 40 generates theA, B, C, and D signals and inputs them in the S/H circuits 41 to 44.Then, the S/H wobble processing circuit 40 switches the level of an S/Hswitching signal 46 as shown in (4). Specifically, the S/H wobbleprocessing circuit 40 samples the S/H switching signal 46 in High statein a segment in which the return beam is Low, and holds the S/Hswitching signal 46 Low in a segment in which the return beam is High.Consequently, output level of each of the S/H circuits 41 to 44 becomesLow as shown in (5). As the outputs are inputted in the adders 31 and32, the subtractor 37 produces the (A+D)−(B+C) signal as the wobblesignal.

In this way, conventional compact optical disks obtain a wobble signalby sampling space segments. The S/H wobble processing circuit 40 iscapable of such processing because the wobble signal has a frequency of22.05 KHz which is much lower than the recording data's frequency of 200KHz to 720 KHz, and thus reproduction of the wobble signal is not muchaffected by the S/H process.

Conventional optical disk devices of this type include, for example, theone disclosed in Patent Document 1 described later. The optical diskdevice disclosed in Patent Document 1 performs sampling to reproduce aCD-R/RW wobble signal only when spaces are encountered, and then obtainsa wobble signal by predetermined signal processing.

Besides, optical disk devices which use an LPP signal include, forexample, the one disclosed in Patent Document 2 described later. Theoptical disk device disclosed in Patent Document 2 is mainly intendedfor DVD-R/RW and obtains the LPP signal by performing signal processingseparately for marks and spaces. That is, the marks and spaces areseparately subjected to signal processing, levels of the marks in binaryterms are extracted by an LPF (Low Pass Filter), and AC voltages areadded. Also, levels of the spaces in binary terms are sampled alone andextracted by an LPF, and AC voltages are added. Signals obtained by theadditions of the AC voltages are binarized by a comparator, resultingvalues are ANDed, and thereby an LPP signal for each segment isdetected. Finally, the LPP signals are ORed, and thereby LPP signals inboth mark and space segments are reproduced.

However, conventional optical disk devices have the following problems.Since the technique disclosed in JP2002-216355A (pp. 5-7, FIG. 1;hereinafter referred to as Patent Document 1) samples only spacesegments being recorded, if LPP signals which serve as a reference forrecording and reproducing operations are inserted as in the case ofDVD-R/RW or the like, although the LPP signal recorded in the spacesegments can be reproduced, the LPP signal recorded in the mark segmentscannot be reproduced.

Also, in the case of DVD+R/RW, since there is no land pre-pit and thewobble signal contains address information, the wobble signal must bereproduced with high quality. However, when the wobble signal andrecording data are close in frequency as is the case with DVD+R/RW, ifspace segments alone are sampled, it is difficult to detect the wobblesignal and thus it is not possible to reproduce high-quality wobblesignal.

The technique disclosed in JP10-283638A (pp. 5-7, FIG. 1; hereinafterreferred to as Patent Document 2) can reproduce only the LPP signal, andcannot reproduce the wobble signal.

That is, other means must be used to reproduce the wobble signal. Thus,in view of the above problems, it can be seen that the wobble signal andLPP signal should be reproduced both in mark segments and spacesegments. During recording on an optical disk, laser intensity variesbetween mark segments and space segments and naturally return beamintensity varies as well. Thus, in principle, the gain can be switchedquickly in sync with return beams. To switch the gain, there is known,for example, a gain-switching wobble processing circuit 50 shown in FIG.14.

Switching operation of the gain-switching wobble processing circuit 50will be described with reference to a timing chart in FIG. 15. It isassumed here that the optical disk is a compact disk.

During recording, a waveform of a writing beam shown in (2) becomes Highor Low depending on whether recording data shown in (1) is High or Low.Consequently, a waveform of a return beam goes High by rising sharply asshown in (3).

As a photodetector detects a return beam with such a waveform, thegain-switching wobble processing circuit 50 generates A, B, C, and Dsignals and inputs them in gain switching circuits 51 to 54. Then, thegain-switching wobble processing circuit 50 switches the level of again-switching signal 56 as shown in (4). Specifically, thegain-switching wobble processing circuit 50 switches the gain by settingthe switching signal 56 High (increase the gain) in a segment in whichthe waveform of the return beam is Low and setting the switching signal56 Low (decreases the gain) in a segment in which the waveform of thereturn beam is High. Consequently, the output level of the gainswitching circuits 51 to 54 becomes constant in all segments as shown in(5). As the outputs are inputted in adders 31 and 32, a subtractor 37produces an (A +D)−(B+C) signal as the wobble signal and LPP signal.

However, when the gain is switched quickly, although there is no problemif there is no timing offset between the gain switching and the returnbeam as in the case of segment SE1, if there is a timing offset betweenthe gain switching and the return beam as in the case of segment SE2,unnecessary pulsed signal components such as those indicated by P1 andP2 are included when the gain is switched, degrading the quality of thewobble signal and LPP signal.

To solve this problem, the gain should be switched very quickly withhighly accurate timing. Actually, however, it is difficult to achievesuch timing adjustment in view of temperature variations and the like.

A write-once medium such as −R or +R contains much noise at thebeginning of recording segments due to a large input signal orelectrical overshoot. This may degrade signal quality.

The present invention has been made in view of the above problems andhas an object to provide an optical disk device, circuit for an opticaldisk device, wobble signal reproduction method, and land pre-pit signalreproduction method which can reproduce a wobble signal and LPP signalwith high quality.

DISCLOSURE OF THE INVENTION

According to claim 1 of the present invention, there is provided anoptical disk device which reproduces a wobble signal, i.e., informationabout wobbling of the tracks, from an optical disk that hasinformation-recording tracks formed spirally from inner radius to outerradius of the disk, wobbling periodically, characterized by comprising:mark forming means which forms marks on the tracks by laser irradiationaccording to recording data; a split-type optical sensor which outputsmultiple systems of signals by detecting return beams from the marks aswell as from spaces between the marks; first sampling means whichsamples, in mark segments, the signals outputted from the split-typeoptical sensor and outputs the sampled signals; second sampling meanswhich samples, in space segments, the signals outputted from thesplit-type optical sensor and outputs the sampled signals; and selectionmeans which alternately selects and outputs the signals sampled andoutputted by the first and second sampling means.

Thus, in DVD+R/RW or the like which uses a wobble signal, signalsobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. The signals from themarks and spaces can be combined properly by combining the signalsoutputted alternately.

According to claim 2 of the present invention, there is provided anoptical disk device which reproduces a land pre-pit signal from anoptical disk that has information-recording tracks formed spirally frominner radius to outer radius of the disk, wobbling periodically, withland pre-pits for reproduction of address information being formedbetween the tracks, characterized by comprising: mark forming meanswhich forms marks on the tracks by laser irradiation according torecording data; a split-type optical sensor which outputs multiplesystems of signals by detecting return beams from the marks as well asfrom spaces between the marks; first sampling means which samples, inmark segments, the signals outputted from the split-type optical sensorand outputs the sampled signals; second sampling means which samples, inspace segments, the signals outputted from the split-type optical sensorand outputs the sampled signals; and selection means which alternatelyselects and outputs the signals sampled and outputted by the first andsecond sampling means.

Thus, in DVD-R/RW or the like which uses a wobble signal, a signalobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. The signals from themarks and spaces can be combined properly by combining the signalsoutputted alternately.

According to claim 3 of the present invention, the optical disk deviceaccording to claim 1 is characterized by comprising reproducing meanswhich adds the multiple systems of signals subjected to a series ofprocesses by the first sampling means, the second sampling means, andthe selection means, in predetermined combinations, finds differencesamong the added signals after justifying amplitudes of the addedsignals, and thereby reproduces the wobble signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe wobble signal by combining the signals from the marks and spacesproperly.

According to claim 4 of the present invention, the optical disk deviceaccording to claim 3 is characterized by comprising reproducing meanswhich adds the multiple systems of signals subjected to a series ofprocesses by the first sampling means, the second sampling means, andthe selection means, in predetermined combinations, finds differencesamong the added signals after justifying amplitudes of the addedsignals, and thereby reproduces the land pre-pit signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe land pre-pit signal by combining the signals from the marks andspaces properly.

According to claim 5 of the present invention, the optical disk deviceaccording to claim 1 or 2 is characterized by comprising first amplitudeadjusting means which justifies amplitudes of the signals sampled andoutputted by the first sampling means.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

According to claim 6 of the present invention, in the optical diskdevice according to claim 5, the first amplitude adjusting meanscontrols gain based on difference between light quantity of a returnbeam from the marks and light quantity of a return beam from the spaces.

This makes it possible to justify the amplitudes of the sampled signalswith high accuracy.

According to claim 7 of the present invention, the optical disk deviceaccording to claim 1 or 2 is characterized by comprising secondamplitude adjusting means which justifies amplitudes of the signalssampled and outputted by the second sampling means.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

According to claim 8 of the present invention, in the optical diskdevice according to claim 7, the second amplitude adjusting meanscontrols gain based on difference between light quantity of a returnbeam from the marks and light quantity of a return beam from the spaces.

This makes it possible to justify the amplitudes of the sampled signalswith high accuracy.

According to claim 9 of the present invention, the optical disk deviceaccording to claim 1 or 2 is characterized by comprising timinggenerating means which generates a control signal for use to controltiming for the first sampling means to sample the signals outputted fromthe split-type optical sensor in mark segments, a control signal for useto control timing for the second sampling means to sample the signalsoutputted from the split-type optical sensor in space segments, and acontrol signal for use to control timing for the selection means toalternately select the signals outputted from the first and secondsampling means, according to the recording data.

This makes it possible to properly control the operation of sampling thesignals in mark segments and space segments and selecting and outputtingthem alternately, where the signals are obtained by detecting the returnbeams from the marks and spaces of the optical disk.

According to claim 10 of the present invention, in the optical diskdevice according to claim 1 or 2, when the signals from the marks aresampled by the first sampling means, sampling segments are set shorterthan signal segments of the marks so that the sampling segments will fitin the signal segments; and when the signals from the spaces are sampledby the second sampling means, sampling segments are set shorter thansignal segments of the spaces so that the sampling segments will fit inthe signal segments.

Thus, the signals obtained by detecting the return beams from the marksand spaces of the optical disk can be sampled reliably in the marksegments and space segments.

According to claim 11 of the present invention, in the optical diskdevice according to claim 1 or 2, both the first and second samplingmeans have a switch used to sample the signals outputted from thesplit-type optical sensor and a capacitor connected to an output end ofthe switch and used to hold the sampled signals.

This makes it possible to implement the sampling means with a simpleconfiguration consisting of a switch and capacitor.

According to claim 12 of the present invention, in the optical diskdevice according to claim 1 or 2, the first sampling means samples thesignals in the mark segments by turning on the switch and charging thecapacitor with electrical charge of the signals outputted from thesplit-type optical sensor and holds the signals in the spaces by turningoff the switch and outputting the electrical charge; and the secondsampling means samples the signals in the spaces by turning on theswitch and charging the capacitor with electrical charge of the signalsoutputted from the split-type optical sensor and holds the signals inthe marks by turning off the switch and outputting the electricalcharge.

This makes it possible to implement the sampling means which samples andholds the signals outputted from the split-type optical sensor, with asimple configuration consisting of a switch and capacitor.

According to claim 13 of the present invention, in the optical diskdevice according to claim 1 or 2, the first sampling means has a lowpass filter.

This makes it possible to remove sharp noise components liable to occuron rising edges of marks.

According to claim 14 of the present invention, in the optical diskdevice according to claim 1 or 2, the selection means has a switch usedto alternately select the signals sampled and outputted by the first andsecond sampling means and a capacitor used to hold the selected signals.

This makes it possible to implement the selection means with a simpleconfiguration consisting of a switch and capacitor.

According to claim 15 of the present invention, there is provided acircuit for an optical disk device intended for an optical disk whichhas information-recording tracks formed spirally from inner radius toouter radius of the disk, wobbling periodically, where the optical diskdevice forms marks on the tracks by laser irradiation according torecording data, outputs multiple systems of signals by detecting returnbeams from the marks as well as from spaces between the marks using asplit-type optical sensor, and thereby reproduces a wobble signal, i.e.,information about wobbling of the tracks, characterized by comprising:first sampling means which samples, in mark segments, the signalsoutputted from the split-type optical sensor and outputs the sampledsignals; second sampling means which samples, in space segments, thesignals outputted from the split-type optical sensor and outputs thesampled signals; and selection means which alternately selects andoutputs the signals sampled and outputted by the first and secondsampling means.

Thus, in DVD+R/RW or the like which uses a wobble signal, a signalobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. The signals from themarks and spaces can be combined properly by combining the signalsoutputted alternately.

According to claim 16 of the present invention, there is provided acircuit for an optical disk device intended for an optical disk whichhas information-recording tracks formed spirally from inner radius toouter radius of the disk, wobbling periodically, with land pre-pits forreproduction of address information being formed between the tracks,where the optical disk device forms marks on the tracks by laserirradiation according to recording data, outputs multiple systems ofsignals by detecting return beams from the marks as well as from spacesbetween the marks using a split-type optical sensor, and therebyreproduces a wobble signal, i.e., information about wobbling of thetracks, characterized by comprising: first sampling means which samples,in mark segments, the signals outputted from the split-type opticalsensor and outputs the sampled signals; second sampling means whichsamples, in space segments, the signals outputted from the split-typeoptical sensor and outputs the sampled signals; and selection meanswhich alternately selects and outputs the signals sampled and outputtedby the first and second sampling means.

Thus, in DVD-R/RW or the like which uses a wobble signal, a signalobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. The signals from themarks and spaces can be combined properly by combining the signalsoutputted alternately.

According to claim 17 of the present invention, the circuit for anoptical disk device according to claim 15 is characterized by comprisingreproducing means which adds the multiple systems of signals subjectedto a series of processes by the first sampling means, the secondsampling means, and the selection means, in predetermined combinations,finds differences among the added signals after justifying amplitudes ofthe added signals, and thereby reproduces the wobble signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe wobble signal by combining the signals from the marks and spacesproperly.

According to claim 18 of the present invention, the circuit for anoptical disk device according to claim 16 is characterized by comprisingreproducing means which adds the multiple systems of signals subjectedto a series of processes by the first sampling means, the secondsampling means, and the selection means, in predetermined combinations,finds differences among the added signals after justifying amplitudes ofthe added signals, and thereby reproduces the land pre-pit signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe land pre-pit signal by combining the signals from the marks andspaces properly.

According to claim 19 of the present invention, the circuit for anoptical disk device according to claim 15 or 16 is characterized bycomprising first amplitude adjusting means which justifies amplitudes ofthe signals sampled and outputted by the first sampling means.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

According to claim 20 of the present invention, the circuit for anoptical disk device according to claim 15 or 16 is characterized bycomprising second amplitude adjusting means which justifies amplitudesof the signals sampled and outputted by the second sampling means.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

According to claim 21 of the present invention, there is provided awobble signal reproduction method for reproducing a wobble signal, i.e.,information about wobbling of tracks, from an optical disk that hasinformation-recording tracks formed spirally from inner radius to outerradius of the disk, wobbling periodically, characterized by comprising:a first step of forming marks on the tracks by laser irradiationaccording to recording data; a second step of outputting multiplesystems of signals by detecting return beams from the marks formed inthe first step as well as from spaces between the marks, with asplit-type optical sensor; a third step of sampling, in mark segments,the signals outputted from the split-type optical sensor and outputtingthe sampled signals; a fourth step of sampling, in space segments, thesignals outputted from the split-type optical sensor and outputting thesampled signals; and a fifth step of alternately selecting andoutputting the signals sampled and outputted in the first and secondsampling steps.

Thus, in DVD+R/RW or the like which uses a wobble signal, a signalobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. This makes it possibleto reproduce the wobble signal properly from the output signals.

According to claim 22 of the present invention, the wobble signalreproduction method according to claim 21 is characterized by furthercomprising a sixth step of adding the multiple systems of signalssubjected to a series of processes in the third, fourth, and fifthsteps, in predetermined combinations, finding differences among theadded signals after justifying amplitudes of the added signals, andthereby reproducing the wobble signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe wobble signal by combining the signals from the marks and spacesproperly.

According to claim 23 of the present invention, the wobble signalreproduction method according to claim 21 is characterized by furthercomprising a seventh step of justifying amplitudes of the signalssampled and outputted in the mark segments and space segments.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

According to claim 24 of the present invention, there is provided a landpre-pit signal reproduction method for reproducing a land pre-pit signalfrom an optical disk that has information-recording tracks formedspirally from inner radius to outer radius of the disk, wobblingperiodically, with land pre-pits for reproduction of address informationbeing formed between the tracks, characterized by comprising: a firststep of forming marks on the tracks by laser irradiation according torecording data; a second step of outputting multiple systems of signalsby detecting return beams from the marks formed in the first step aswell as from spaces between the marks, with a split-type optical sensor;a third step of sampling, in mark segments, the signals outputted fromthe split-type optical sensor and outputting the sampled signals; afourth step of sampling, in space segments, the signals outputted fromthe split-type optical sensor and outputting the sampled signals; and afifth step of alternately selecting and outputting the signals sampledand outputted in the first and second sampling steps.

Thus, in DVD-R/RW or the like which uses a wobble signal, a signalobtained by detecting return beams from marks and spaces of the opticaldisk are sampled in mark segments and space segments and resultingsignals are selected and outputted alternately. This makes it possibleto reproduce the land pre-pit signal properly from the output signals.

According to claim 25 of the present invention, there land pre-pitsignal reproduction method according to claim 24 is characterized byfurther comprising a sixth step of adding the multiple systems ofsignals subjected to a series of processes in the third, fourth, andfifth steps, in predetermined combinations, finding differences amongthe added signals after justifying amplitudes of the added signals, andthereby reproducing the land pre-pit signal.

Thus, the signals from the marks and spaces are selected alternately,the signals are added, the amplitudes of the added signals arejustified, and the differences among the added signals are found,thereby to reproduce the wobble signal. This makes it possible to obtainthe wobble signal by combining the signals from the marks and spacesproperly.

According to claim 26 of the present invention, there land pre-pitsignal reproduction method according to claim 24 is characterized byfurther comprising a seventh step of justifying amplitudes of thesignals sampled and outputted in the mark segments and space segments.

Thus, the sampled signals are selected alternately after theiramplitudes are justified. Consequently, signals of basically the samepotential are selected alternately, eliminating the need to set switchtiming for the selection accurately or use high switching speed. Thismakes it possible to combine the signals from the marks and spaceseasily and properly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an optical disk device according to anembodiment of the present invention;

FIG. 2 is a diagram showing a configuration example of an S/H circuit ofthe optical disk device according to the embodiment;

FIG. 3 is a diagram showing a configuration example of a mark/spaceselector switch of the optical disk device according to the embodiment;

FIG. 4 is a timing chart illustrating the operation of reproducing anLPP signal on the optical disk device according to the embodiment;

FIG. 5 is a timing chart illustrating the operation of reproducing anwobble signal on the optical disk device according to the embodiment;

FIG. 6 is a diagram showing an example in which the S/H circuit of theoptical disk device according to the embodiment is configured with anLPF;

FIG. 7 is a timing chart illustrating characteristics obtained when theS/H circuit of the optical disk device according to the embodiment isconfigured with the LPF;

FIG. 8 is a diagram showing a configuration of an optical disk;

FIG. 9 is an enlarged view of grooves, lands, and LPP on an opticaldisk;

FIG. 10 is a conceptual view of a photodetector (split-type opticalsensor);

FIG. 11 is a block diagram showing a configuration of an wobbleprocessing circuit;

FIG. 12 is a block diagram showing a configuration of an S/H wobbleprocessing circuit;

FIG. 13 is a timing chart illustrating the operation of sampling andholding return beams by the S/H wobble processing circuit;

FIG. 14 is a block diagram showing a configuration of a gain-switchingwobble processing circuit; and

FIG. 15 is a timing chart illustrating the operation of sampling andholding return beams by the gain-switching wobble processing circuit.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described with referenceto the drawings.

FIG. 1 is a block diagram showing an optical disk device according to anembodiment of the present invention. The optical disk device 60 in FIG.1 comprises an optical disk 10, a photodetector 20 which outputs A, B,C, and D signals by detecting them from the optical disk 10, awobble/LPP reproducing circuit 62 which reproduces a wobble signal andLPP signal from the A, B, C, and D signals outputted from thephotodetector 20, and an LD driver 64 which controls laser intensity(write strategy control) according to recording data during writes tothe optical disk 10. It is assumed here that the optical disk 10 is aDVD-R/RW shown in FIGS. 8 and 9.

The wobble/LPP reproducing circuit 62 comprises a mark/space combiningcircuit 76 a for the A signal, a mark/space combining circuit 76 b forthe B signal, a mark/space combining circuit 76 c for the C signal, amark/space combining circuit 76 d for the D signal, a timing signalgenerator 78, and a wobble processing circuit 80, where each of themark/space combining circuits 76 a, 76 b, 76 c, and 76 d comprises amark S/H circuit 66, an space S/H circuit 68, and amplifiers 70 and 72and mark/space selector switch 74. It is assumed here that the wobbleprocessing circuit 80 is the same as the wobble processing circuit 30shown in FIG. 11.

These components will be described next.

The timing signal generator 78 generates, according to recording data, amark S/H switching signal 84 to be outputted to the mark S/H circuit 66of the mark/space combining circuits 76 a to 76 d for the A, B, C, and Dsignals; a space S/H switching signal 86 to be outputted to the spaceS/H circuit 68; and a mark/space combining signal 88 to be outputted toa mark/space selector switch 74.

The mark/space combining circuit 76 a for the A signal will be describedby representing the mark/space combining circuits 76 a to 76 d for theA, B, C, and D signals.

As shown in FIG. 2, the mark S/H circuit 66 consists of a switch 90which is connected to a signal path and is turned on and off accordingto the mark S/H switching signal 84 and a capacitor 92 connected betweena signal path downstream of the switch 90 and the earth. When the switch90 is ON, the A signal produced by a return beam from marks 12 a on theoptical disk 10 and detected by the photodetector 20 is sampled andoutputted to the amplifier 70. When the switch 90 is OFF, the A signalis held as electrical charge of the A signal stored in the capacitor 92is outputted to the amplifier 70.

The space S/H circuit 68 has the same configuration as the one shown inFIG. 2. It consists of a switch 90 which is connected to a signal pathand is turned on and off according to the space S/H switching signal 86and a capacitor 92 connected between a signal path downstream of theswitch 90 and the earth. When the switch 90 is ON, the A signal producedby a return beam from spaces 12 b on the optical disk 10 and detected bythe photodetector 20 is outputted to the amplifier 70. When the switch90 is OFF, the A signal is held as electrical charge of the A signalstored in the capacitor 92 is outputted to the amplifier 70.

As shown in (5) and (6) of FIG. 4, the mark S/H switching signal 84 andthe space S/H switching signal 86 have a relationship in which when oneof them is High, the other is Low. As shown in a segment SE2 in whichthere is a timing offset, this relationship is such that a segment inwhich the mark S/H switching signal 84 is High fits in a segment inwhich a return beam from marks 12 a shown in (3) is High while a segmentin which the space S/H switching signal 86 is Low is wider than asegment in which the return beam is High.

This is intended to prevent the effect of unnecessary noise by avoidingrising and falling edges even if there is a timing offset duringsampling in a segment in which the return beam is High.

The amplifiers 70 and 72 make gain adjustments according to differencein light quantity between return beams to justify the amplitudes ofoutput signals 101 and 103 processed by the mark S/H circuit 66 andspace S/H circuit 68. Incidentally, the amplitudes of the output signals101 and 103 maybe justified by means of attenuation according to thedifference in light quantity using attenuators instead of the amplifiers70 and 72.

As shown in FIG. 3, the mark/space selector switch 74 consists ofswitches 94 and 96 which are connected to signal output paths of theamplifiers 70 and 72 and are turned on and off according to themark/space combining signal 88, and a capacitor 98 connected between asignal path connected with the output side of the switches 94 and 96 andthe earth. It combines the signals whose amplitudes are justified bygain control of the amplifiers 70 and 72, according to the mark/spacecombining signal 88. In so doing, the switches 94 and 96 select signalsof basically the same potential alternately and combine the selectedsignals, eliminating the need to set switch timing for the selectionaccurately or use high switching speed.

Incidentally, S/H circuits or adders may be used instead of the selectorswitches 94 and 96 shown in FIG. 3 for the mark/space selector switch74.

The operation of reproducing a wobble signal and LPP signal on theoptical disk device 60 will be described with reference to a flowchartin FIG. 4.

First, during recording, in a segment in which recording data shown in(1) is High, i.e., in a segment of High state which specifies a mark 12a to be formed, intensity of a laser beam directed at the optical disk10 is increased by write strategy control performed by the LD driver 64corresponding to the High state, causing a writing beam to provide writepower as shown in (2). Since the optical disk 10 is a DVD-R/RW, thewriting beam has a comb waveform.

The writing beam forms a mark 12 a on the optical disk 10. In so doing,the waveform of a return beam used to read the A and D signals goes Highby rising in the form of mountain ranges as shown in (3) and thewaveform of a return beam used to read the B and C signals goes High byrising in the form of mountain ranges as shown in (4).

On the other hand, in a segment in which recording data is Low, i.e., ina segment of Low state which specifies a space 12 b to be formed,intensity of the laser beam directed at the optical disk 10 is decreased(or turned off) by write strategy control performed by the LD driver 64corresponding to the Low state, causing a writing beam to provide readpower as shown in (2). In so doing, the waveform of a return beam goesLow as shown in (3) and (4). However, there are LPP signal components asindicated by P3 and P4 in the segment in which the return beam is Low.

As the return beams of the waveforms shown in (3) and (4) are detectedby the photodetector 20, the A, B, C, and D signals are generated andsupplied to the mark S/H circuits 66 and space S/H circuits 68 of themark/space combining circuits 76 a to 76 d for the A, B, C, and Dsignals.

At the time when the A, B, C, and D signals whose return beams are Highare supplied to the S/H circuits 66 and 68, the mark S/H switchingsignal 84 and space S/H switching signal 86 generated by the timingsignal generator 78 corresponding to mark segments and space segments ofthe recording data, respectively, go High and Low, respectively, asshown in (5) and (6).

At the time when the mark S/H switching signal 84 goes High and thespace S/H switching signal 86 goes Low, the High state of the mark S/Hswitching signal 84 turns on the switch 90 of the mark S/H circuit 66,and thus the A and D signals of the form corresponding to the combwaveform of the return beam shown in (3) are sampled as shown in (7) andthe output signal 101 of the mark S/H circuit 66 goes High correspondingto the High-state, comb waveform of the return beam. Also, since the Lowstate of the space S/H switching signal 86 turns off the switch 90 ofthe space S/H circuit 68, the output signal 103 of the space S/H circuit68 is held in Low state as shown in (8).

Conversely, at the time when the mark S/H switching signal 84 goes Lowand the space S/H switching signal 86 goes High as shown in (5) and (6),the Low state of the mark S/H switching signal 84 turns off the switch90 of the mark S/H circuit 66, and thus the output signal 101 of themark S/H circuit 66 is held in Low state as shown in (7). Also, sincethe High state of the space S/H switching signal 86 turns on the switch90 of the space S/H circuit 68, the Low-state, A and D signals of thereturn beam shown in (3) including the LPP signal component P3 aresampled, causing the output signal 103 of the space S/H circuit 68 to goLow with the LPP signal component P3 included as shown in (8).

Although the S/H process has been described citing only the S/H processof the A and D signals in (7) and (8), the B and C signals similarly gothrough the S/H process.

After the S/H process, the output signals 101 and 103 have theiramplitudes justified to a fixed level by gain control of the amplifiers70 and 72 and are combined by the mark/space selector switch 74 whichcontrols combination according to the mark/space combining signal 88.Consequently, as shown in (9), the mark/space combining circuit 76 a forthe A signal outputs a Low-state, combined mark/space signal A1containing comb waveforms in High state and an LPP signal component P3a. Similarly, the mark/space combining circuit 76 d for the D signaloutputs a Low-state, combined mark/space combining signal D1 containingcomb waveforms in High state and an LPP signal component P3 a.

Also, as shown in (10), the mark/space combining circuit 76 b for the Bsignal outputs a Low-state, combined mark/space signal B1 containingcomb waveforms in High state and an LPP signal component P4 a.Similarly, the mark/space combining circuit 76 c for the C signaloutputs a Low-state, combined mark/space signal C1 containing combwaveforms in High state and an LPP signal component P4 a.

The combined mark/space signal A1 is synthesized from only thatcomponents (High-state, comb waveforms) of the output signal 101 of themark S/H circuit 66 which are sampled and indicated by a solid line in(7) and that components (Low-state waveforms including the LPP signalcomponent P3 a) of the output signal 103 of the space S/H circuit 68which are sampled and indicated by a solid line in (8), and it does notcontain the held components indicated by dotted lines in (7) and (8).This is because the mark/space selector switch 74 causes only sampledsignal components to be outputted out of the output signal 101 of themark S/H circuit 66 and the output signal 103 of the space S/H circuit68. Since the reliable, sampled signal components excluding the heldcomponents are combined in this way, the combined mark/space signal A1has high quality. The same is true to the other combined mark/spacesignals B1 to D1.

The combined mark/space signals A1 to D1 are processed by the wobbleprocessing circuit 80 to reproduce an LPP signal 105 shown in (11).

A wobble signal 107 is not shown in FIG. 4 used to describe thereproduction of the LPP signal 105 because it differs greatly infrequency scale. The wobble signal 107 has a waveform illustratedexaggeratedly in FIG. 5.

Specifically, a sin wave which is a wobble signal component issuperimposed on the entire return beam as shown in (3) and (4) of FIG.5, and thus the wobble signal component is superimposed on both mark andspace output signals 101 and 103 shown in (7) and (8) of FIG. 5 as wellas on the combined mark/space signals A1 to D1 shown in (9) and (10) ofFIG. 5.

Then, as the combined mark/space signals A1 to D1 are processed by thewobble processing circuit 80, the sine-wave wobble signal 107 isreproduced as shown in (11) of FIG. 5.

Thus, with the optical disk device 60 according to this embodiment, themark S/H circuit 66 samples a signal A generated as the photodetector 20detects a return beam from the marks 12 a of the optical disk 10, thespace S/H circuit 68 samples a signal A generated as the photodetector20 detects a return beam from the spaces 12 b, and the amplitudes of thesampled A signals from the marks and spaces are justified by theamplifiers 70 and 72. The mark and space signals whose amplitudes havebeen justified are selected alternately and combined by the mark/spaceselector switch 74. After the A, B, C, and D signals from thephotodetector 20 are subjected to a series of processes up to thecombination process, the wobble processing circuit 80 adds them inpredetermined combinations, finds differences among the added signalsafter justifying the amplitudes of the added signals, and therebyreproduces the wobble signal 107 and LPP signal 105.

That is, the signal from the marks 12 a is sampled, the signal from thespaces 12 b is sampled, the amplitudes of the sampled signals arejustified, and then the signals are combined by being selectedalternately. Consequently, signals of basically the same potential arecombined by being selected alternately, eliminating the need to setswitch timing for the selection accurately or use high switching speed.This makes it possible to combine the signals from the marks and spaceseasily and properly.

Also, since the signal sampling segments of the marks 12 a are setshorter than the signal segments of the marks 12 a so that the samplingsegments will fit in the signal segments and the signal samplingsegments of the spaces 12 b are set shorter than the signal segments ofthe spaces 12 b so that the sampling segments will fit in the signalsegments, the signals from the marks 12 a and spaces 12 b can be sampledreliably.

Consequently, the signal sampling segments of the marks 12 a and spaces12 b are set apart from each other, making it possible to avoid risingand falling edges of the signal in the marks 12 a during sampling evenif there is a timing offset. This in turn makes it possible to preventthe effect of unnecessary noise which would be produced if the risingand falling edges are sampled.

Thus, the wobble signal 107 and LPP signal 105 can be reproduced withhigh quality.

Besides, the mark S/H circuit 66 and space S/H circuit 68 maybe equippedwith an LPF (Low Pass Filter). For example, a resistor 110 may be addedto the input side of the switch 90 as shown in FIG. 6.

The use of the mark/space S/H circuits equipped with an LPF produces thefollowing effects. When a return beam contains sharp rising edgesindicated by P5 and P6 as shown in a timing chart (1) in FIG. 7, if thereturn beam is sampled using the mark S/H switching signal 84 shown in(2) of FIG. 7, the use of a mark S/H circuit 66 without an LPF causesthe sharp rising edges indicated by P5 and P6 to remain as noise, asindicated by P5 a, P6 a, and P6 b in (3) of FIG. 7.

However, the use of mark/space S/H circuits equipped with an LPF makesit possible to remove the sharp rising edges P5 and P6 with the LPF asshown in (4) of FIG. 7. Thus, both wobble signal and LPP signal can bereproduced with high quality.

INDUSTRIAL APPLICABILITY

A signal generated through the detection of a return beam from marks ofan optical disk is sampled, a signal generated through the detection ofa return beam from spaces is sampled, the amplitudes of the sampledsignals are justified, and the signals are combined by being selectedalternately. That is, signals of basically the same potential arecombined by being selected alternately, eliminating the need to setswitch timing for the selection accurately or use high switching speed.This makes it possible to combine the signals from the marks and spaceseasily and properly.

1. An optical disk device which reproduces a wobble signal, i.e.,information about wobbling of tracks, from an optical disk that hasinformation-recording tracks formed spirally from inner radius to outerradius of the disk, wobbling periodically, characterized by comprising:mark forming means which forms marks on the tracks by laser irradiationaccording to recording data; a split-type optical sensor which outputsmultiple systems of signals by detecting return beams from the marks aswell as from spaces between the marks; first sampling means whichsamples, in mark segments, the signals outputted from the split-typeoptical sensor and outputs the sampled signals; second sampling meanswhich samples, in space segments, the signals outputted from thesplit-type optical sensor and outputs the sampled signals; and selectionmeans which alternately selects and outputs the signals sampled andoutputted by the first and second sampling means.
 2. An optical diskdevice which reproduces a land pre-pit signal from an optical disk thathas information-recording tracks formed spirally from inner radius toouter radius of the disk, wobbling periodically, with land pre-pits forreproduction of address information being formed between the tracks,characterized by comprising: mark forming means which forms marks on thetracks by laser irradiation according to recording data; a split-typeoptical sensor which outputs multiple systems of signals by detectingreturn beams from the marks as well as from spaces between the marks;first sampling means which samples, in mark segments, the signalsoutputted from the split-type optical sensor and outputs the sampledsignals; second sampling means which samples, in space segments, thesignals outputted from the split-type optical sensor and outputs thesampled signals; and selection means which alternately selects andoutputs the signals sampled and outputted by the first and secondsampling means.
 3. The optical disk device according to claim 1,characterized by comprising reproducing means which adds the multiplesystems of signals subjected to a series of processes by the firstsampling means, the second sampling means, and the selection means, inpredetermined combinations, finds differences among the added signalsafter justifying amplitudes of the added signals, and thereby reproducesthe wobble signal.
 4. The optical disk device according to claim 2,characterized by comprising reproducing means which adds the multiplesystems of signals subjected to a series of processes by the firstsampling means, the second sampling means, and the selection means, inpredetermined combinations, finds differences among the added signalsafter justifying amplitudes of the added signals, and thereby reproducesthe land pre-pit signal.
 5. The optical disk device according to claim 1or 2, characterized by comprising first amplitude adjusting means whichjustifies amplitudes of the signals sampled and outputted by the firstsampling means.
 6. The optical disk device according to claim 5,characterized in that the first amplitude adjusting means controls gainbased on difference between light quantity of a return beam from themarks and light quantity of a return beam from the spaces.
 7. Theoptical disk device according to claim 1 or 2, characterized bycomprising second amplitude adjusting means which justifies amplitudesof the signals sampled and outputted by the second sampling means. 8.The optical disk device according to claim 7, characterized in that thesecond amplitude adjusting means controls gain based on differencebetween light quantity of a return beam from the marks and lightquantity of a return beam from the spaces.
 9. The optical disk deviceaccording to claim 1 or 2, characterized by comprising timing generatingmeans which generates a control signal for use to control timing for thefirst sampling means to sample the signals outputted from the split-typeoptical sensor in mark segments, a control signal for use to controltiming for the second sampling means to sample the signals outputtedfrom the split-type optical sensor in space segments, and a controlsignal for use to control timing for the selection means to alternatelyselect the signals outputted from the first and second sampling means,according to the recording data.
 10. The optical disk device accordingto claim 1 or 2, characterized in that: when the signals from the marksare sampled by the first sampling means, sampling segments are setshorter than signal segments of the marks so that the sampling segmentswill fit in the signal segments; and when the signals from the spacesare sampled by the second sampling means, sampling segments are setshorter than signal segments of the spaces so that the sampling segmentswill fit in the signal segments.
 11. The optical disk device accordingto claim 1 or 2, characterized in that both the first and secondsampling means have a switch used to sample the signals outputted fromthe split-type optical sensor and a capacitor connected to an output endof the switch and used to hold the sampled signals.
 12. The optical diskdevice according to claim 11, characterized in that: the first samplingmeans samples the signals in the marks by turning on the switch andcharging the capacitor with electrical charge of the signals outputtedfrom the split-type optical sensor and holds the signals in the spacesby turning off the switch and outputting the electrical charge; and thesecond sampling means samples the signals in the spaces by turning onthe switch and charging the capacitor with electrical charge of thesignals outputted from the split-type optical sensor and holds thesignals in the marks by turning off the switch and outputting theelectrical charge.
 13. The optical disk device according to claim 1 or2, characterized in that both the first and second sampling means have alow pass filter.
 14. The optical disk device according to claim 1 or 2,characterized in that the selection means has a switch used toalternately select the signals sampled and outputted by the first andsecond sampling means and a capacitor used to hold the selected signals.15. A circuit for an optical disk device intended for an optical diskwhich has information-recording tracks formed spirally from inner radiusto outer radius of the disk, wobbling periodically, where the opticaldisk device forms marks on the tracks by laser irradiation according torecording data, outputs multiple systems of signals by detecting returnbeams from the marks as well as from spaces between the marks using asplit-type optical sensor, and thereby reproduces a wobble signal, i.e.,information about wobbling of the tracks, characterized by comprising:first sampling means which samples, in mark segments, the signalsoutputted from the split-type optical sensor and outputs the sampledsignals; second sampling means which samples, in space segments, thesignals outputted from the split-type optical sensor and outputs thesampled signals; and selection means which alternately selects andoutputs the signals sampled and outputted by the first and secondsampling means.
 16. A circuit for an optical disk device intended for anoptical disk which has information-recording tracks formed spirally frominner radius to outer radius of the disk, wobbling periodically, withland pre-pits for reproduction of address information being formedbetween the tracks, where the optical disk device forms marks on thetracks by laser irradiation according to recording data, outputsmultiple systems of signals by detecting return beams from the marks aswell as from spaces between the marks using a split-type optical sensor,and thereby reproduces a land pre-pit signal, characterized bycomprising: first sampling means which samples, in mark segments, thesignals outputted from the split-type optical sensor and outputs thesampled signals; second sampling means which samples, in space segments,the signals outputted from the split-type optical sensor and outputs thesampled signals; and selection means which alternately selects andoutputs the signals sampled and outputted by the first and secondsampling means.
 17. The circuit for an optical disk device according toclaim 15, characterized by comprising reproducing means which adds themultiple systems of signals subjected to a series of processes by thefirst sampling means, the second sampling means, and the selectionmeans, in predetermined combinations, finds differences among the addedsignals after justifying amplitudes of the added signals, and therebyreproduces the wobble signal.
 18. The circuit for an optical disk deviceaccording to claim 16, characterized by comprising reproducing meanswhich adds the multiple systems of signals subjected to a series ofprocesses by the first sampling means, the second sampling means, andthe selection means, in predetermined combinations, finds differencesamong the added signals after justifying amplitudes of the addedsignals, and thereby reproduces the land pre-pit signal.
 19. The circuitfor an optical disk device according to claim 15 or 16, characterized bycomprising first amplitude adjusting means which justifies amplitudes ofthe signals sampled and outputted by the first sampling means.
 20. Thecircuit for an optical disk device according to claim 15 or 16,characterized by comprising second amplitude adjusting means whichjustifies amplitudes of the signals sampled and outputted by the secondsampling means.
 21. A wobble signal reproduction method for reproducinga wobble signal, i.e., information about wobbling of tracks, from anoptical disk that has information-recording tracks formed spirally frominner radius to outer radius of the disk, wobbling periodically,characterized by comprising: a first step of forming marks on the tracksby laser irradiation according to recording data; a second step ofoutputting multiple systems of signals by detecting return beams fromthe marks formed in the first step as well as from spaces between themarks, with a split-type optical sensor; a third step of sampling, inmark segments, the signals outputted from the split-type optical sensorand outputting the sampled signals; a fourth step of sampling, in spacesegments, the signals outputted from the split-type optical sensor andoutputting the sampled signals; and a fifth step of alternatelyselecting and outputting the signals sampled and outputted in the firstand second sampling steps.
 22. The wobble signal reproduction methodaccording to claim 21, characterized by further comprising a sixth stepof adding the multiple systems of signals subjected to a series ofprocesses in the third, fourth, and fifth steps, in predeterminedcombinations, finding differences among the added signals afterjustifying amplitudes of the added signals, and thereby reproducing thewobble signal.
 23. The wobble signal reproduction method according toclaim 21, characterized by further comprising a seventh step ofjustifying amplitudes of the signals sampled and outputted in the marksegments and space segments.
 24. A land pre-pit signal reproductionmethod for reproducing a land pre-pit signal from an optical disk thathas information-recording tracks formed spirally from inner radius toouter radius of the disk, wobbling periodically, with land pre-pits forreproduction of address information being formed between the tracks,characterized by comprising: a first step of forming marks on the tracksby laser irradiation according to recording data; a second step ofoutputting multiple systems of signals by detecting return beams fromthe marks formed in the first step as well as from spaces between themarks, with a split-type optical sensor; a third step of sampling, inmark segments, the signals outputted from the split-type optical sensorand outputting the sampled signals; a fourth step of sampling, in spacesegments, the signals outputted from the split-type optical sensor andoutputting the sampled signals; and a fifth step of alternatelyselecting and outputting the signals sampled and outputted in the thirdand fourth sampling steps.
 25. The land pre-pit signal reproductionmethod according to claim 24, characterized by further comprising asixth step of adding the multiple systems of signals subjected to aseries of processes in the third, fourth, and fifth steps, inpredetermined combinations, finding differences among the added signalsafter justifying amplitudes of the added signals, and therebyreproducing the land pre-pit signal.
 26. The land pre-pit signalreproduction method according to claim 24, characterized by furthercomprising a seventh step of justifying amplitudes of the signalssampled and outputted in the mark segments and space segments.